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GLERL 2001 Milestone Reports
GOAL: IMPLEMENT SEASONAL TO INTERANNUAL CLIMATE FORECASTS
OBJECTIVE 3: Conduct Research for Improved Climate Predictions
PM: Improve understanding of atmospheric, oceanic, land surface and cryospheric processes that contribute to seasonal-to-interannual climate variability, as measured by peer-reviewed publications form NOAA-supported research
Milestone: Assessing impacts of projected greenhouse warming on Great Lakes regional water resources.
Scientist: B. Lofgren, GLERL
Purpose: The risk of changes in the mean water level of the Great Lakes as a result of increased greenhouse gases poses a variety of threats to the human economics associated with the Great Lakes system and their ecology. Although previous studies (Croley 1990) have been carried out using a similar methodology to that used here, the methods in the general circulation model (GCM) simulations used here as input have progressed significantly. The new main features include the use of transient scenarios, in which the amount of atmospheric CO2 is gradually increased, rather than suddenly doubled, atmospheric coupling to a full dynamical ocean model, and the inclusion of the direct effect of sulfate aerosols on solar radiation.
Efforts: This project was carried out as part of the Great Lakes Regional Assessment Group of the National Climate Change Impacts Assessment. More information on GLERL's portion of this study can be found in the assessment group's summary report (Lofgren et al. 2000). A more complete version will appear in Lofgren et al. (2001). The National Climate Change Impacts Assessment concentrated on simulating the changes in various important systems within the United States that would result from the climate changes predicted by two GCMs: the Canadian Centre for Climate Modelling and Analysis Coupled General Circulation Model version 1 (CGCM1) and the Hadley Climate Centre (UK) Climate Model version 2 (HadCM2). We used three future times as primary benchmarks: 20-year periods centered about the years 2030, 2050 and 2090.
The resulting data were processed to remove biases relative to the observed climate data, then input to GLERL's suite of land surface runoff/evaporation models for the Great Lakes Basin and lake evaporation and thermodynamics models for the lakes themselves, in order to determine the overall net basin supply for each of the lakes (precipitation minus evaporation over the lake plus runoff from the rivers tributary to it). The time series of net basin supply, in turn, were used as input to the channel routing model, which calculates the amount of flow between the lakes and the water levels, which are regarded as the ultimate result of this study.
The two GCMs that were used as input gave quite different results. The CGCM1 yielded large increases in air temperatures (which are a large determining factor in evaporation both from the lakes and from the land in the drainage basin) and generally some increase in precipitation (Figure 1). The net results were drops in lake levels for all of the lakes and all of the time periods investigated, up to a maximum drop of 1.38 m over Lake Michigan-Huron in 2090. On the other hand, the HadCM2 predicted smaller increases in air temperature and greater increases in precipitation. In terms of lake level, there were small drops in lake level predicted for Lake Superior in 2030 and 2050, but mostly lake level rises, up to 0.35 m over Lake Michigan-Huron in 2090 (Figure 1).
Figure 1. Chart of changes in level of Lake Michigan-Huron as predicted using general circulation model results in the current study and previous studies. The current study's results are the CGCM1 for 2030 and 2090 (points 5 and 12, respectively) and HadCM2 for 2030 and 2090 (points 6 and 11). The abscissa represents the percentage change over the Lake Michigan-Huron basin in annual mean precipitation and the ordinate represents the change in annual mean temperature over the basin. The size of the symbol (oval for drop, hourglass for rise) represents the relative magnitude in the change of lake level from the present case to the future scenario.
Customers: The results of this study have created much interest among representatives of the Great Lakes shipping and recreational boating industries, as well as the media. Demonstrative of this was the meeting on March 30, 2001 at the offices of the Environmental Protection Agency in Chicago, which highlighted the results of this study of climate change impacts on lake levels, and included additional speakers on the consequences of reduced lake levels to the lake shipping industry and the hazards of recreational boating. Attendees included representatives of various governmental bodies and coalitions, non-governmental organizations, industrial organizations, and media outlets. There was an article published in the Chicago Tribune that very day and another distributed by the Associated Press the next day. Other customer concerns include hydroelectric power generation and lake regulation, with much interest shown by the International Joint Commission. Many of the impacts on lake levels, net basin supply, and onset and cessation of thermal stratification of the lakes were used by other sections of the Great Lakes Regional Assessment Group, notably the lake ecology section (Lehman et al. 2000).
Significance: The significance of this study is reflected in the interest of the customers listed above. The uncertainty that is exposed in the difference between the results using the CGCM1 and those using the HadCM2 is something to take note of. Customers are advised to be prepared for changes in either direction, but because the possibility shown for lower lake levels is more extreme and because low lake levels have not been experienced in the last few decades, preparation for low lake levels is to be emphasized.
Success: This study has set some new marks for expected changes in Great Lakes levels due to increasing atmospheric concentrations of greenhouse gases over the next century. It has raised the caution flag that changes in lake levels may be anywhere from slightly positive to strongly negative.
Next steps: Further study related to this will take two prongs: study of the results of changing variability in climate as predicted by GCMs and the use of a regional climate model that couples the atmosphere over the Great Lakes Basin to the lake thermodynamics. The former will be an extension of the Great Lakes regional climate change assessment, using the same GCMs as input, but breaking them down into time series with the model's non-stationary internal time variability intact. The latter is currently underway, using the Coupled Hydrosphere-Atmosphere Research Model (CHARM), with lateral boundary conditions supplied by CGCM1.
References:
Croley, T. E., II 1990. Laurentian Great Lakes double-CO2 climate change hydrological impacts. Climatic Change, 17:27-47.
Lehman, J. T., A. S. Brooks, and J. C. Zastrow 2000. Water ecology. In Preparing for a Changing Climate: The Potential Consequences of Climate Variability and Change: Great Lakes Overview, P. J. Sousounis and J. M. Bisanz, eds., pp. 43-49. U.S. Global Change Research Program.
Lofgren, B. M., F. H. Quinn, A. H. Clites, R. A. Assel, and A. J. Eberhardt 2000. Water resources. In Preparing for a Changing Climate: The Potential Consequences of Climate Variability and Change: Great Lakes Overview, P. J. Sousounis and J. M. Bisanz, eds., pp. 29-37. U.S. Global Change Research Program.
Lofgren, B. M., F. H. Quinn, A. H. Clites, R. A. Assel, A. J. Eberhardt, and C. L. Luukkonen 2001. Climate change impacts on Great Lakes Basin water resources. J. Great Lakes Res., in press.
Last updated: August 8, 2002 mbl